d) 82 seconds, same as (b) but with plastic fan sprayer
e) 81 seconds, same as (b) but with plastic quick connect stop with male stub
f) 102 seconds, same as (b) extended with ~30' of 3/8" ID rubber air hose.

Accuracy is probably +-2 seconds

Our only pattern of use will be one outlet at a time.

The idea is to route garden hoses to various locations in the yard to supply fixed spigots with attached quick connects. Watering will be done by turning on the house faucet, then using a short length of 3/8" ID rubber air hose carried from spigot to spigot as needed, then turning off the house faucet. The hoses will be buried in the duff, or under a few inches in the dirt. A short length of garden hose from an outside faucet will supply a nearby manifold which will in turn supply the various buried hoses.

We're not concerned about draining for winter freezes. We've had one hose attached continuously for 8 years without a freeze problem. Our outside faucets are the $5 kind and we don't insulate them in the winter.

We're not worried about rodents chewing the hoses.

From the measurements of flow rates, for example (a) versus (b), it seems not to matter which hose ID's I choose to bury, and the connectors and cutoffs don't matter either. I also have a long roll of 3/4" polyethelene I could use.

Is there something I am not considering in choosing 5/8" hoses over 3/4" hoses or the 3/4" polyethylene?

3/4” is 1/8” larger than 5/8”. If you add quick couplers or shutoff valves etc, it’s really a flow restrictor too. If you look at many of those devices they limit flow down to 1/4 or 3/8 as the water passes that point, making it a flow restrictor. As such any larger hose size after the flow restrictor won’t carry full flow. The 5 gallon bucket test is excellent for determining flow rates, but for apples to apples comparison, watch out adding things that restrict flow like quick couplers, shutoff valves and multi port manifolds.
– TysonMay 1 '18 at 19:16

I did post post fill times for quick-connects and shutoff valves. The main flow loss is due to the length 3/8" air hose (20% slower with 30 feet of it)
– MichelleMay 1 '18 at 19:19